Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
As the fuel gas supplied to the fuel cell, normally, a hydrogen gas and CO generated from hydrocarbon raw material by a reformer are used. In general, in the reformer, a reformed raw material gas is obtained from hydrocarbon raw material of a fossil fuel or the like, such as methane or LNG, and the reformed raw material gas undergoes steam reforming, partial oxidation reforming, or autothermal reforming to produce a reformed gas (fuel gas).
The solid oxide fuel cell (SOFC) is a fuel cell operated at high temperature. For example, when supply of the fuel gas is stopped during operation, the anode is oxidized, and the fuel cell may be degraded undesirably.
In this regard, for example, a fuel cell system described in Japanese Laid-Open Patent Publication No. 2006-066244 includes detection means for detecting a state where no fuel is supplied to the fuel cell, and emergency stop means for emergently stopping operation of the fuel cell when the detection means detects that no fuel is supplied to the fuel cell.
However, in the technique described in Japanese Laid-Open Patent Publication No. 2006-066244, as the emergency stop means, a tank filled with an inert gas needs to be provided in the fuel cell system. Therefore, the fuel cell system is complicated, and the overall size of the fuel cell system becomes large. The cost of providing the fuel cell system is high.